This invention relates to compatible storage-stable mixtures containing relatively high molecular weight polyhydroxyl compounds and short chained polyols and to their use for the preparation of the polyurethanes. The invention also relates to the use of these storage-stable mixtures in two-component polyurethane adhesives.
It is known from DE-B-1,770,703 to use incompatible polyols for the preparation of polyurethane mixtures. End products having improved properties such as, for example, good heat resistance and high impact strength, are obtainable by these means.
However, the use of a mixture of incompatible polyols has various disadvantages with regard to storage and processing. Even a brief period of storage, i.e. several hours to 3 days, of thoroughly mixed polyol systems results in separation of the mixture into two phases. Thus the polyol mixtures must be intensively mixed each time before they are filled into containers or they must be continuously mixed or kept in circulation to ensure that the ratio of components in the mixture will be kept constant.
Various methods have become known for stabilizing the phases of such mixtures.
According to the teaching of U.S. Pat. No. 3,945,939, for example, the phases may be sedimented by the addition of colloidal silica or a clay which has been modified with an onium compound. DE-A 2,341,294 similarly teaches the use of inert, surface-active materials having a specific surface area of from 10 to 800 m.sup.2 /g, such as a silica agglomerate and/or a chrysotile asbestos and/or an inorganic material similar to chrysotile asbestos in its mineral structure.
Another possibility of homogenizing several polyols which are incompatible with one another comprises of adding liquid or soluble solubilizing agents. Thus, according to U.S. Pat. No. 4,141,952, mixtures of monomeric polyols having a molar mass of &lt;500 and polyether polyols having a molar mass of from 1800 to 7000 are prevented from separating by using so-called graft polypropylene ether glycols in the molar mass range of from 1500 to 3500.
A stable emulsion of a high molecular weight polyol and ethylene glycol or butanediol-(1,4) is prepared according to U.S. Pat. No. 4,273,884 by adding an ethylene oxide/propylene oxide copolymer (molar mass 12,000).
Mixtures of poly(oxypropylene/oxyethylene) polyols (OH number 20 to 60) having certain oxyethylene contents with ethylene glycol or butanediol are described in DE-B 2,759,398. The polyols used must contain from 10 to 30% by weight of oxyethylene end groups and from 5 to 60% by weight of inner oxyethylene groups. The polyols should preferably contain as much inner ethylene oxide as possible.
According to U.S. Pat. No.-B 471,405, mixtures of high molecular weight polyoxyalkylene polyols having OH equivalent weights of from 650 to 3000 and ethylene glycol, for example, are prevented from separating by means of soluble diol compounds such as 1,2-butylene glycol, di-(1,2-butylene glycol), di-(1,2-propylene glycol) and tri-(1,2-propylene glycol).
It is also known to one skilled in the art that diphasic mixtures of incompatible polyols may be stabilized as a single phase by the addition of emulsifiers such as long chain benzene alkyl sulphonates, etc.
None of these teachings of the prior art it completely satisfactory. The use of solids as emulsion stabilizers is liable to cause abrasion of the dosing and mixing apparatus and the stabilizing effect generally diminishes sharply after only a few days. Moreover, there are objections to the use of materials containing asbestos on physiological grounds. When surface-active substances are used it is necessary to take into account their intrinsic catalytic activities, in particular when charged with onium compounds.
The use of so-called "graft polyols" proposed in U.S. Pat. No. 4,141,852 has the disadvantage in that "graft polyols" are expensive compared with ungrafted polyols, thus rendering the process less economical.
The teaching of U.S. Pat. No. 4,273,884 also fails to satisfy the demand for a single phase, storage-stable polyol mixture since the emulsions which can be prepared thereby show signs of at least partial phase separation within the first 6-8 weeks. The above Patent Specification merely maintains that "fairly stable" emulsions are obtained.
Although such monophasic stable polyol mixtures can be produced by means of di- and tripropylene glycols according to U.S. Pat. No. 471,405, it is well known to one skilled in the art that the addition of these compounds results in a severe deterioration in the mechanical properties of the polyurethane parts produced, in particular a loss of dimensional stability under heat.
The use of conventional emulsifiers for obtaining a single phase polyol mixtures has numerous disadvantages. The emulsifiers are liable to separate as crystals from the polyol mixture in the course of time or they may, for example, accumulate on the surface, and may alter the catalytic balance of the system in an uncontrollable manner and may bleed out of the polyurethane parts and hence drastically impair its use properties.
There is, therefore still an urgent technical need for polyol or polyol-polyamine formulations which are stable in storage for a sufficient period of time, have a high hydroxyl number of the mixture, possibly a high hydroxyl/amine number, and optionally also contain a high proportion of preferably low molecular weight chain lengthening agents.
DE-A 3,219,759 teaches that the compatibility of (i) relatively high molecular weight polyoxyalkylene polyols in the OH number range of from 20 to 210 containing at least 5% by weight of predominantly terminal oxyethylene segments with (ii) ethylene glycol may be established by modifying ethylene glycol with from 0.1 to 0.5 mol of propylene oxide per mol of ethylene glycol.
DE-A 3,219,822 (=EP-A-0,095,635) teaches that the compatibility produced by the propoxylation of ethylene glycol (and/or of 1,4-butanediol, which may also be used as a low molecular weight diol) may be enhanced by incorporating in the mixtures certain ammonium or metal salts of the type also used according to the invention.
EP-0,150,427 describes the use of potassium salts as compatibility imparting agents. The salts proposed include inter alia the product of addition of potassium hydrogen sulphite to 2-cis-butenediol-(1,4) followed by a reaction with propylene oxide as solubilizing agent. It does not teach the use of 2-cis-butenediol-(1,4) itself as solubilizing agent.
U.S. Pat. No. 4,786,435 describes the use of phenols as compatibility imparting agents for RIM systems.
U.S. Pat. No. 4,839,087 teaches the use of urethanes as compatibility imparting agents for RIM systems. U.S. Pat. No. 4,673,696 describes the use of unsaturated esterols such as fumaric acid or maleic acid esters as compatibility imparting agents. It teaches their use in RIM systems. EP-A 0,341,375 describes the use of mixtures of polyoxypropylenetriols in storage-stable RIM systems. The mixtures may be free from polyoxyethylene contents in the polyether.
U.S. Pat. No. 4,385,133 describes compatible mixtures of glycols and propylene oxide/ethylene oxide polyols requiring a high minimum proportion of ethylene oxide groups. The mixtures may be used in RIM systems. U.S. Pat. No. 4,319,973 describes polyurethane elastomers which are prepared using storage-stable mixtures of certain polymer polyols with glycols. Their use is limited to certain ethylene oxide contents and certain compositions of the polymer polyols.
U.S. Pat. No. 4,576,731 describes mixtures of polyols whose compatibility is improved by a reaction with isocyanates.
Two-component polyurethane adhesives have long been known. U.S. Pat. No. 3,274,160 describes reaction products of polyisocyanates with a mixture which has alcoholic hydroxyl functions. U.S. Pat. No. 3,591,561 and 3,725,355 describe the preparation of polyurethane elastomers. In the former case, a lactone polyester polyol and a low molecular weight diol are reacted with an organic diisocyanate and cross-linked by means of a diamine or polyol such as glycerol. In the latter case, the polyurethane elastomer is obtained from a polyether polyol, a chain-lengthening agent and an isocyanate prepolymer with the aid of a tin catalyst. U.S. Pat. No. 3,577,295 describes polyurethane elastomers for driving belts, using polyol mixtures containing polymers of unsaturated monomers, organic polyisocyanates and amines as hardeners. U.S. Pat. No. 4,182,898 describes polyurethanes of polyester polyol prepolymers which are reacted with diisocyanates together with low molecular weight polyols. U.S. Pat. No. 4,193,832 describes the reaction of polyisocyanates with isocyanate-reactive hydrogen in which tertiary amines may function as catalysts. A process of preparation of polyurethane adhesives using excess diisocyanates, polyols and optionally chain lengthening agents such as, for example, amines is described in U.S. Pat. No. 4,156,064. The use of amines for rendering adhesives non-sagging is particularly described in U.S. Pat. No. 3,979,364, 4,336,298 and 4,444,976 and in EP-A-63,534.
U.S. Pat. No. 4,487,909 describes an adhesive based on a polyol, e.g. a polyether polyol, and glycerol as branching agent. U.S. Pat. No. 4,530,941 describes a RIM polyurethane mixture composed of a high molecular weight polyol, a chain lengthening agent, a polyoxyalkylene having amino end groups and a polyisocyanate. U.S. Pat. No. 4,554,340 describes the polyol mixture for the preparation of polyurethanes from high molecular weight polyalkylene oxide and low molecular weight diol and optionally also isocyanate reactive compounds such as glycerol and diamine. U.S. Pat. No. 4,568,717 described the preparation of polyols from organic polyisocyanates with a terephthalic acid polyester polyol.
U.S. Pat. No. 3,714,127 describes two-component polyurethane adhesives based on an isocyanate prepolymer to which an amine is added for increasing the viscosity and to ensure non-sagging.
EP-A-0,068,209 describes a two-component polyurethane adhesive having a polyol component containing a polyester or polyether triol, a phenylene diamine and a tin catalyst. This mixture is reacted with an aromatic diisocyanate.
EP-A-248,254 describes a two-component polyurethane adhesive which is a reaction product of a hydroxyl functional material, a di- or triamine and an organic isocyanate. The adhesives prepared by this method are distinguished by outstanding properties but do not satisfy all demands as regards stability of the polyol component in storage.
It is therefore an object of the present invention to provide compatible mixtures of relatively high molecular weight polyhydroxyl compounds and short-chained polyols and polyamines which constitute efficient two-component adhesive systems when mixed with isocyanates.